Bohdan V. Oliinyk

A special electronic tongue system based on photoelectric measurements on Si–Si/SiN_X sensitive structures is reported. The sensing approach is based on measuring of minority carrier lifetime in silicon-based substrates using microwave-detected photoconductance decay. This inexpensive and environmentally friendly combinatorial electronic sensing platform is able to create characteristic electronic fingerprints of liquids, detect, and recognize them. In particular, an application of the optoelectronic tongue for recognition of vegetable oils and their mixtures is described.

Critical analysis of the data reported by Zhong et al. (J. Am. Chem. Soc. 2013, 135 (22), 8350–8356)1 is carried out. In particular, one of the main results of Zhong et al. concerning the formation of photoluminescent silicon nanoparticles (Si NPs) in an aqueous solution of (3-aminopropyl) trimethoxysilane (APTMS) and trisodium citrate dihydrate (Na3Cit) under microwave heating is impugned. These results are reconsidered here because of what appear to be significant inaccuracies and misinterpretations that have been spread through a wide number of other subsequent publications.

The problem of silicon substrate selection for the sensor structure based on deep junction barrier has been investigated. The described sensor is functioning on photoelectrical conversion principle for the illumination with has high absorption coefficient in the silicon. The method of substrate pre-selection with the measurement of capacitance-voltage characteristics has been suggested. As shape of the capacitance-voltage curves in the system liquid analyte/silicon substrate (with or without chemically modified silicon surface) highly depends on charge state of the interface and near-surface band bending, some recommendation for silicon substrate choosing can be used. The obtained results indicate that the shift of the saturation voltage of the capacitance-voltage curves correlates with peculiarities of photocurrent distribution in the deep silicon barrier structure. Based on the results of the research the effective recombination sensors with reproducible characteristics can be fabricated.

The porous silicon (PS) surface modification diagnostics due to functionalization and water adsorption/desorption processes were provided by the self-action effects of picosecond range pulsed laser radiation at 1064 nm. It was shown that the PS surface functionalization—oxide removal, alkylation, and oxidation—resulted in a refractive nonlinear optical (NLO) response sign turn to self-focusing (Δn>0) versus the self-defocusing (Δn<0) observed in the aged PS. The sensitivity of the proposed technique was revealed to water adsorption/desorption from the chemically oxidized PS interface. For the dried PS, the self-defocusing effect with corresponding NLO cubic susceptibility Re(χ (3))∼−4.7·10−9 esu was observed versus the self-focusing one (∼5·10−8 esu) for the PS positioned in saturated water vapor at room temperature. The obtained results demonstrate high sensitivity and wide versatility of the proposed readout technique based on pulsed laser radiation self-action at 1064 nm to the PS surface modification monitoring/diagnostics applications.

Introduction of hydrofluoric acid before and during chemical functionalization of silicon nanocrystals with hydrocarbon chains is found to be very efficient for removing original surface defects of the nanocrystals as well as for preserving them from oxidation induced defects appearing on their surface during photoinitiated hydrosilylation procedure. In consequence, stable sols of highly luminescent silicon quantum dots in organic solvents with photoluminescence quantum yield up to 20% are shown to be easily obtained. Moreover, our approach allows considerable improvement of electric transport through meso-porous silicon nanostructures which is still a serious challenge for their applications in photovoltaics and thermoelectrics. Finally, the use of hydrofluoric acid appears as a cheap and efficient alternative to development of painstaking procedures and set-ups preventing oxidation induced deterioration of physico-chemical properties of the individual and interconnected silicon nanocrystals during their chemical functionalization.

The conformational behaviour of model peptides containing a 2-pyrrolidinemethanesulfonic acid (2PyMS) residue was studied in both the crystalline state and in solution using X-ray, NMR and IR experiments. It was found that in crystals dipeptide PhC(O)–2PyMS–Phe–NHiPr adopted β-turn conformation, which was not stabilized by an intramolecular hydrogen bond and could be classified as a type IV β-turn. In the crystalline state tripeptide PhC(O)–Ala–2PyMS–Phe–NHiPr existed as an α-turn with uncommon cis-conformation of the amide bond formed by the pyrrolidine nitrogen atom of the 2PyMS residue, for which no close analogue can be envisaged among the tight turns identified so far. Although the tendency to adopt folded conformations was only partially retained in solution, 2-PyMS could be considered as a promising structural unit for the design of foldamers and peptidomimetics with unusual conformational properties.